Many current electronic systems utilize a semiconductor die attached to a next level package. A current technique for attaching a semiconductor die to a next level package is known as the controlled chip collapse connection, or C4. In the C4 technique, the semiconductor die is bonded to the next level package with interconnects. The interconnects are heated to form the bond, a process commonly known as reflowing. Heating the interconnects is achieved by heating the die, next level package, and interconnects simultaneously in a reflow oven at elevated temperatures.
While this method is effective for bonding the semiconductor die to the next level package, it can result in mechanical stresses in the assembly so produced as a result of differing coefficients of thermal expansion between the semiconductor die and the next level package materials. If the semiconductor die and the next level package have different coefficients of thermal expansion, they will not expand or contract to the same extent when heated or cooled through the same temperature range in the reflow oven. After being removed from the reflow oven and cooling, the resulting assembly can thus suffer from residual mechanical stresses which are greater than desired.